Development and Comparison of Intramuscularly Injected Long-acting Testosterone Undecanoate Nano-/Microcrystal Suspensions with Three Different Particle Size

The aim of this study was to develop and compare the pharmacokinetic property of testosterone undecanoate (TU) nano-/microcrystal suspension with three different particle sizes after intramuscular (i.m.) administration. TU nano-/microcrystal suspensions were prepared by high pressure homogenization method and the mean particle size was 0.30 ± 0.11 μm (A), 1.21 ± 0.37 μm (B), and 4.83 ± 0.60 μm (C), respectively. Scanning electron microscope (SEM) was employed to observe the morphology of nano-/microcrystal suspensions after operation. X-ray Powder diffraction (XRPD) confirmed the crystalline state of TU in nano-/microcrystal suspension. After storage at 4 °C and 25 °C under mechanical shaking for 2 months, physical and chemical stabilities of nano-/microcrystal suspensions were measured by particle size analyzer and high performance liquid chromatography. There was no obvious change in particle size distribution and content of TU. After i.m. administration of suspension C to rats, the concentration of TU in plasma lasted for nearly 12 days that was comparative with the commercial testosterone undecanoate injection. The results showed that microcrystal C with a larger particle size had long-acting effect comparing with other two suspensions. The muscle irritation test in rabbits showed that the local irritation of TU nano-/microcrystal suspensions was lower than that of commercial testosterone undecanoate injection. It can be concluded that appropriate particle size of nano-/microcrystal suspensions for i.m. administration of TU was important to achieve better therapeutic effect.